Fine-grained logs of programmers’ activities serve as research material in various fields of computer science. For activities in a traditional environment, there is a publicly available dataset. However, to our knowledge, no comparable dataset exists for activities in a cell-based computational notebook environment. This paper presents an open dataset of activities in the Jupyter Notebook. The dataset comprises the activity logs of 21 programmers who worked on a one-hour data science task in our log collection experiment. The dataset would contribute to understanding programmers’ workflows in cell-based notebook environments and evaluating proposals for those environments.